JPH0590241A - Method of processing si substrate - Google Patents

Abstract

PURPOSE:To process a non-porous Si substrate and to bore holes to penetrate the substrate from the substrate surface to the substrate rear in an arbitrary form and in an arbitrary size. CONSTITUTION:A method of processing an Si substrate has a process for bringing partially a non-porous Si substrate 51 into a porous state from the substrate surface to the substrate rear at one place or more and a process for etching selectively and removing porous Si regions 53 only by wetting the substrate, in which non-porous Si regions 51 and the porous Si regions 53 are mixed, in a buffered hydrofluoric acid or a mixed solution obtainable by adding at least one kind of an alcohol and hydrogen peroxide water to the buffered hydrofluoric acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a Si substrate, and more particularly to a method for processing a Si substrate capable of efficiently and uniformly processing a Si substrate with high accuracy. INDUSTRIAL APPLICABILITY The present invention can be applied to processing of semiconductor devices, light transmissive substrates, and micromechanical mechanisms.

[0002]

2. Description of the Related Art In recent years, research has been conducted on a micromechanical mechanism for processing and manufacturing a Si substrate. As a method for etching the bulk Si, chemical etching, reactive ion etching (RIE) is used.
ing) and electrolytic polishing are well known.

The chemical etching method is a resist, Si ₃ N
_This is a method in which the Si substrate is soaked in an etching solution using ₄ or SiO ₂ as a mask to etch only the portion not covered by the mask.

The reactive ion etching method is a resist,
In this method, Si ₃ N ₄ or SiO _{2 is used} as a mask in a reactive ion atmosphere to etch only a portion not covered with the mask.

The electropolishing method is a method in which Si is used as an electrode in an HF solution, a KOH solution or the like to remove Si by an electrolysis reaction. Well known method is rare HF
Anodic etching (Anodic Et), in which Si is etched by an electrolysis reaction on the anode side when a current is passed in a solution using Si as an anode and platinum or gold as a cathode.
ching).

[0006]

However, in the above-described bulk Si etching method, there is no difference in material between the region to be etched and the region not to be etched.
An etching mask having excellent etching resistance is required.

[0007] In chemical etching, overetching occurs in the lateral direction, and in anisotropic etching, a low etching rate surface appears, and it is impossible to form an etching portion only by a wall surface perpendicular to the surface. Further, the shape also changes depending on the plane orientation of the Si substrate.

By the reactive ion etching method, vertical etching can be performed, but it is almost impossible to cut through Si having a thickness of several hundred μm to several mm.

In the electropolishing method, since an electric current is applied, it is difficult to provide an insulating material other than a mask or a semiconductor layer on the front surface or the back surface before etching.

An object of the present invention is to provide a method for processing a Si substrate, which can easily and uniformly process bulk Si and can be applied to a light transmissive substrate, micromachining and the like.

[0011]

Means and Actions for Solving the Problems Si of the Present Invention
The method of processing the substrate is a step of partially making the non-porous Si substrate porous from one surface to the back surface, and a substrate in which the non-porous Si region and the porous Si region are mixed is buffered hydrofluoric acid. , Or buffered hydrofluoric acid with alcohol,
A step of selectively etching and removing only the porous Si region by immersing it in a mixed solution containing at least one kind of hydrogen peroxide water.

The operation of the present invention will be described below.
First, in order to facilitate understanding of the present invention, porous Si used in the present invention and a conventional etching method thereof will be described.

Porous Si is described in 1956 by Uhlir et al.
It was discovered in the process of research on electropolishing of semiconductors in 2010 (A.
Uhlir, Bell Syst.Tech.J., vol 35, p.333 (1956)). Also, Unami et al. Studied the dissolution reaction of Si in anodization and reported that the anodic reaction of Si in HF solution requires holes, and the reaction is as follows (T .
Unagami: J. Electrochem. Soc., Vol.127, p.476 (198
0)).

Si + 2HF + (2-n) e ⁺ → SiF ₂ + 2H ⁺ + ne ^- SiF ₂ + 2HF → SiF ₄ + H ₂ SiF ₄ + 2HF → H ₂ SiF ₆ or Si + 4HF + (4 -λ) e ⁺ → SiF ₄ + 4H ⁺ + λe ^- SiF ₄ + 2HF → H ₂ SiF ₆ Here, e ⁺ and e ⁻ represent holes and electrons, respectively. In addition, n and λ are the numbers of holes required for dissolving Si1 atoms, respectively, and porous Si is formed when the condition of n> 2 or λ> 4 is satisfied.

As described above, holes are required to produce porous Si, and P-type Si is more easily transformed into porous Si than N-type Si.

However, if N-type Si is also injected with holes,
It is known to change into porous Si (RPHolmst
rom and JYChi. Appl. Phys. Lett. Vol. 42,386 (1983)
). This porous Si layer has a density of single crystal Si of 2.33.
By changing the HF solution concentration to 50 to 20% as compared with g / cm ³ , its density is 1.1 to 0.6 g / cm ^3.
The range can be changed. This porous Si layer has an average of about 600 as observed by a transmission electron microscope.
A hole with a diameter of about angstrom is formed. Although its density is less than half that of single crystal Si, single crystallinity is maintained, and it is possible to epitaxially grow a single crystal Si layer on the upper part of the porous layer.

Generally, when a single crystal of Si is oxidized, its volume is increased by about 2.2 times, but by controlling the density of porous Si, it is possible to suppress the volume expansion of the single crystal and to prevent warpage of the substrate. It is possible to avoid cracks introduced into the surface residual single crystal layer. The volume ratio R of the single crystal Si after being oxidized to the porous Si can be expressed as follows.

R = 2.2 × (A / 2.33) where A is the density of porous Si. If R = 1,
That is, when there is no volume expansion after oxidation, A = 1.0
6 (g / cm ³ ) and the density of the porous Si layer is 1.0
When it is 6, volume expansion can be suppressed.

Further, since the porous layer has a large amount of voids formed therein, its density is reduced to less than half. As a result, the surface area increases dramatically compared to the volume,
Its chemical etching rate is significantly enhanced compared to the etching rate of the non-porous Si layer.

Next, the removal of the porous Si by etching will be described.

At present, as far as all the porous Si is concerned, the subsequent steps (epitaxial growth and oxidation) are carried out in the as-produced form, and the porous Si itself is not processed. The reason for this is that it is difficult to process and remove the porous Si with good control. That is, no example has been reported yet in which the etching of the porous Si was performed with good control.

In general, P = (2.33-A) /2.33 is called Porosity, and this value is 30 to 55 during anodization.
%, The porous Si oxide is converted into single crystal S
The quality can be similar to that of the oxide film of i. Porosity
Is P = (m1 −m2) / (m1 −m3) or P = (m1 −m2) / ρAt m1: Total weight before anodization m2: Total weight after anodization m3: Porous Si removed The total weight afterwards is ρ: density of single crystal Si A: area of porosity t: thickness of porous Si, but in many cases the area of the area to be porosity cannot be calculated accurately. In this case, P = (m1
Although -m2) / (m1-m3) is effective, porous Si must be etched in order to measure m3.

In the epitaxial growth on the porous Si described above, because of the structural property of the porous Si, it is possible to relax the strain generated during the heteroepitaxial growth and suppress the generation of defects. .. However, also in this case, it is clear that the Porosity of the porous Si is a very important parameter. Therefore, the above-mentioned measurement of Porosity is indispensable also in this case.

The method for etching porous Si includes: Etch porous Si with NaOH aqueous solution (G.
Bonchil, R. Herino, K. Barla, and JCPfister, J. Electr
ochem.Soc., vol.130, no.7, 1611 (1983)). ． The porous Si is etched with an etchant capable of etching the non-porous Si. It has been known.

[0025] The above method is usually an etching solution of hydrofluoric nitric acid is used, the etching process of the Si in this case, the _{Si + 2O → Si O 2 Si} O 2 +4 HF → Si F 4 + H 2 O As shown, Si is oxidized by nitric acid to be transformed into SiO ₂ , and the SiO ₂ is etched with hydrofluoric acid, whereby the etching of Si proceeds.

However, in the case of etching as in the above method, although porous Si can be etched, non-porous Si is also etched.

Similarly, as a method for etching non-porous Si, there are ethylenediamine type, KOH type, hydrazine type, etc. in addition to the above-mentioned hydrofluoric / nitric acid type etching solution.

From these facts, in order to perform the selective etching of porous Si, it is necessary to select an etching solution other than the above non-porous Si etching solution that can etch porous Si.

The conventional selective etching of porous Si is only etching using the above-mentioned method using an aqueous solution of NaOH as an etching solution.

However, conventionally used NaOH
In the porous Si selective etching method using an aqueous solution,
Adsorption of Na ions on the etching surface is unavoidable. This Na ion is a substance that is a main cause of impurity contamination, is mobile, and has an adverse effect such as forming an interface state, and must not be introduced in a semiconductor process.

The present invention has been made under such a technical background. The operation of the present invention will be described below.

As described above, since the porous layer has a large amount of voids formed therein, the density is reduced to less than half. As a result, the surface area is dramatically increased as compared with the volume, so that the chemical etching rate is significantly increased as compared with the etching rate of the non-porous layer.

The present invention makes use of such properties of porous Si, and Si using an etching solution capable of selectively etching the porous Si with respect to single crystal Si.
A method of processing a substrate is provided.

The feature of the present invention is that the non-porous S
The i substrate is partially made porous from the front surface to the back surface in one or more places, and the non-porous Si region and the porous Si region in which the etching rate is remarkably increased as compared with the non-porous Si region are mixed. By immersing the substrate in an etching solution capable of selectively etching porous Si (buffered hydrofluoric acid or a mixed solution of buffered hydrofluoric acid and at least one of alcohol and hydrogen peroxide solution added) , Selectively removing the porous Si region by etching.

The etching solution used in the present invention is buffered hydrofluoric acid or a mixed solution of buffered hydrofluoric acid and at least one of alcohol and hydrogen peroxide water added, and such etching solution is extremely contaminated. The porous Si can be selectively etched efficiently and uniformly without etching the non-porous Si without adversely affecting the semiconductor process.

In particular, by adding alcohol, the bubbles of the reaction product gas due to etching can be instantly removed from the etching surface without stirring, and the porous Si can be uniformly and efficiently etched. it can.

Further, in particular, by adding hydrogen peroxide solution, the oxidation of Si can be accelerated and the reaction rate can be accelerated as compared with the case of no addition, and the ratio of hydrogen peroxide solution can be further changed. Thus, the reaction rate can be controlled.

The porous Si used in the present invention is
Since it is formed along the current flow during anodization, it is possible to control the current flow by providing a mask or impurity distribution, and to create and process non-porous Si in almost any shape. Is possible.

Further, according to the present invention, a porous Si region is removed extremely efficiently and highly accurately without using an etching preventive film, and a hole is partially penetrated to the back surface of the non-porous Si substrate at one or more places. Can be opened.

[0040]

Embodiments Embodiments of the present invention will be described below. [Embodiment 1] First, the etching solution used in the present invention will be described.

5 to 8 show porous Si and non-porous S.
i Separately for each, buffered hydrofluoric acid, mixed solution of buffered hydrofluoric acid and alcohol, mixed solution of buffered hydrofluoric acid and hydrogen peroxide solution, and buffered hydrofluoric acid, alcohol and hydrogen peroxide solution The etching characteristics with the mixed solution are shown respectively.

Porous Si is produced by anodizing single crystal Si and the conditions are as follows. The starting material of porous Si formed by anodization is not limited to single crystal Si, and Si having another crystal structure is also possible.

Applied voltage: 2.6 (V) Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 2.4 (hours) Thickness of porous Si: 300 (μm) Porosity: 56 (%) In FIG. 5, porous Si and non-porous single crystal Si are infiltrated in buffered hydrofluoric acid, The etching time dependence of the thickness of the porous Si and single crystal Si etched when stirred is shown.

The porous Si prepared under the above conditions was buffered with hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature.
₄ F + H ₂ O) (white circle), and the mixture was stirred. After that, the decrease in the thickness of the porous Si was measured. Porous Si
Is rapidly etched and has a high surface property of 70 μm in about 40 minutes and 118 μm after 120 minutes, and is uniformly etched. The etching rate depends on the solution concentration and the temperature.

In addition, 500 μm thick single crystal Si was buffered with hydrofluoric acid (4.5% HF + 36% NH ₄₎ at room temperature.
F + H ₂ O) (black circle) was infiltrated and stirred. Later,
The reduction in thickness of the single crystal Si was measured. Single crystal Si is
Even after 120 minutes had passed, the etching was less than 100 angstroms.

FIG. 6 shows the porous Si and the non-porous single crystal Si which are infiltrated into the mixed solution of buffered hydrofluoric acid and alcohol without stirring, and the etched porous Si and the single crystal Si. The etching time dependence of the thickness of crystalline Si is shown.

The porous Si prepared under the above conditions was buffered with hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature.
₄ F + H ₂ O) and alcohol mixture (10: 1)
(White circle) was infiltrated without stirring. After that, the decrease in the thickness of the porous Si was measured. Porous Si was rapidly etched, reaching 67 μm in 40 minutes, and 12
After 0 minutes, it has a high surface property of 112 μm and is uniformly etched. The etching rate depends on the solution concentration and the temperature.

In particular, by adding alcohol, the bubbles of the reaction product gas by etching can be instantaneously removed from the etching surface without stirring, and the porous Si can be uniformly and efficiently etched. it can.

Further, 500 μm-thick single crystal Si was buffered with hydrofluoric acid (4.5% HF + 36% NH ₄₎ at room temperature.
It was infiltrated into a mixed solution (10: 1) of F + H ₂ O) and alcohol (black circles) without stirring. After that, the decrease in the thickness of the single crystal Si was measured. Single crystal Si is 120
Even after a lapse of minutes, the etching amount was less than 100 Å.

In FIG. 7, porous Si and non-porous single crystal Si are soaked in a mixed solution of buffered hydrofluoric acid and hydrogen peroxide solution, and the porous Si is etched when stirred.
And shows the etching time dependence of the thickness of single crystal Si.

The porous Si prepared under the above conditions was buffered with hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature.
₄ F + H ₂ O) and 30% hydrogen peroxide solution (1 :)
5) (white circle) was infiltrated and stirred. After that, the decrease in the thickness of the porous Si was measured. Porous Si is rapidly etched and has a high surface property of 88 μm in about 40 minutes and 147 μm in 120 minutes, and is evenly etched. The etching rate is the solution concentration and
Depends on temperature.

In particular, by adding hydrogen peroxide water, the oxidation of Si can be accelerated and the reaction rate can be increased as compared with no addition, and by changing the ratio of hydrogen peroxide water. , Its reaction rate can be controlled.

In addition, 500 μm thick single crystal Si was buffered with hydrofluoric acid (4.5% HF + 36% NH ₄₎ at room temperature.
F + H ₂ O) and 30% hydrogen peroxide solution (1 :)
5) (black circle) was infiltrated and stirred. After that, the decrease in the thickness of the single crystal Si was measured. The single crystal Si was etched by 100 angstroms or less even after 120 minutes.

In FIG. 8, etching was performed when porous Si and non-porous single crystal Si were soaked in a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide solution without stirring. The etching time dependence of the thickness of porous Si and single crystal Si is shown.

The porous Si prepared under the above conditions was buffered with hydrofluoric acid (4.5% HF + 36% NH 3) at room temperature.
₄ F + H ₂ O), alcohol and a 30% hydrogen peroxide solution (10: 6: 50) (white circles) were infiltrated without stirring. After that, the decrease in the thickness of the porous Si was measured. Porous Si is rapidly etched, 83 μm in about 40 minutes, and 140 μm in 120 minutes.
Also has a high degree of surface properties and is uniformly etched.
The etching rate depends on the solution concentration and the temperature.

In particular, by adding alcohol, the bubbles of the reaction product gas due to the etching can be instantly removed from the etching surface without stirring, and the porous Si can be uniformly and efficiently etched. it can.

Further, in particular, by adding hydrogen peroxide solution, the oxidation of Si can be accelerated and the reaction rate can be increased as compared with the case of no addition, and the ratio of hydrogen peroxide solution can be changed. Can control the reaction rate.

In addition, 500 μm thick single crystal Si was buffered with hydrofluoric acid (4.5% HF + 36% NH ₄₎ at room temperature.
F + H ₂ O), alcohol and a 30% hydrogen peroxide solution (10: 6: 50) (black circles) were infiltrated without stirring. After that, the decrease in the thickness of the single crystal Si was measured. Single crystal Si is 100 after 100 minutes.
Only less than Angstrom was etched.

When porous Si and single crystal Si after etching with the above-described etching solution were washed with water and the surface thereof was microanalyzed by secondary ions, no impurities were detected.

The solution concentration of the hydrogen peroxide solution is 30% here, but it is set at a concentration that does not impair the effect of adding the hydrogen peroxide solution and is practically acceptable in the manufacturing process and the like.

The conditions of the solution concentration and the temperature are set within a range in which the effect of the buffered hydrofluoric acid and the hydrogen peroxide solution or the alcohol is exhibited, and the etching rate is practically acceptable in the manufacturing process and the like.

In the present application, the case of the above-mentioned solution concentration and room temperature is taken up as an example, but the present invention is not limited to such conditions.

The HF concentration in the buffered hydrofluoric acid is set within the range of preferably 1 to 95%, more preferably 1 to 85%, further preferably 1 to 70% with respect to the etching solution. The NH ₄ F concentration in the acid is set within the range of preferably 1 to 95%, more preferably 5 to 90%, and further preferably 5 to 80% with respect to the etching solution.

The H ₂ O ₂ concentration is
It is preferably 1 to 95%, more preferably 5 to 90%, still more preferably 10 to 80%, and is set within a range in which the effect of the hydrogen peroxide solution is exhibited.

The alcohol concentration is set to preferably 80% or less, more preferably 60% or less, still more preferably 40% or less with respect to the etching solution and within the range in which the effect of the alcohol is exhibited.

The temperature is preferably set in the range of 0 to 100 ° C, more preferably 5 to 80 ° C, and further preferably 5 to 60 ° C.

As the alcohol used in the present invention, in addition to ethyl alcohol, isopropyl alcohol and other alcohols that have practically no adverse effect on the production process and can be expected to have the above alcohol addition effect can be used.

Next, a method of processing a Si substrate using the above etching solution will be described.

FIG. 1 shows an example in which both the front and back surfaces of non-porous Si are partially covered with a mask and the exposed portion is made porous from the front surface to the back surface.

As shown in FIG. 1A, non-porous Si5
Both the front and back surfaces of 1 are covered with a mask 52, and a window is partially opened. Here, as the mask, a polyimide film having high resistance to buffered hydrofluoric acid, apiezon wax, a high resistance epitaxial film, a high resistance non-epitaxial deposition film, or the like is used.

Next, the exposed portion is made porous from the front surface to the back surface (FIG. 1 (b)). At this time, the porous Si region 5
Since 3 is formed along the current flow during anodization, the mask 52 allows the porous Si region to be formed in an almost arbitrary shape.

Thereafter, the mask 52 is peeled off, and only the porous Si is selectively removed by wet chemical etching using one of the above four kinds of etching solutions. Of course, the mask may be peeled off after the porous Si region 53 is selectively etched. Further, when the mask 52 does not have any adverse effect on the application of the processed product, such as an epitaxial layer, it is clear that the mask 52 need not be peeled off.

FIG. 1C shows a completed diagram of this embodiment. As described above, the holes can be partially penetrated from the front surface to the back surface of the non-porous Si at one or more locations.

Here, if the mask is arranged at the same position on the front surface and the back surface in the same plane, the wall surface of the hole becomes vertical to the front surface, and if it is arranged so as to be displaced, the wall surface becomes oblique. [Embodiment 2] FIG. 2 shows an example in which the surface of non-porous Si is partially covered with a mask and the exposed portion to the back surface is made porous.

As shown in FIG. 2A, non-porous Si6
The surface of 1 is covered with a mask 62, and a window is partially opened. Here, as the mask, a polyimide film having high resistance to buffered hydrofluoric acid, apiezon wax, a high resistance epitaxial film, a high resistance non-epitaxial deposition film, or the like is used.

Next, the exposed portion is made porous from the back surface (FIG. 2B).

After that, the mask 62 is peeled off, and only the porous Si region 63 is selectively removed by wet chemical etching using one of the above four kinds of etching solutions.
Of course, the mask 62 may be peeled off after the porous Si region 63 is selectively etched. Further, if the mask 62 does not have any adverse effect on the application of the present processed product such as an epitaxial layer, the mask 62
It is clear that it is not necessary to peel off.

FIG. 2C shows a completed diagram of this embodiment. As described above, the holes can be partially penetrated from the front surface to the back surface of the non-porous Si at one or more locations. [Embodiment 3] FIG. 3 shows an example in which the front surface and the back surface of the non-porous Si are partially made high in resistance, and the exposed low resistance portion is made porous from the front surface to the back surface.

As shown in FIG. 3A, non-porous Si7
The resistance is partially increased on both the front surface and the back surface of No. 1 and the high resistance region 72
To make. At least one low resistance region is exposed on each side. The high resistance region 72 is formed by a non-deposition method such as ion implantation or impurity diffusion.

Next, the exposed low resistance portion is made porous from the front surface to the back surface (FIG. 3B). At this time, porous Si
Since the region 73 is formed along the current flow during anodization, the high resistance region 72 allows the porous Si region to be formed in an almost arbitrary shape.

After that, only one of the above four kinds of etching solutions is used to selectively remove only the porous Si region 73 by wet chemical etching.

FIG. 3C shows a completed diagram of this embodiment. As described above, the holes can be partially penetrated from the front surface to the back surface of the non-porous Si at one or more locations.

Here, if the high resistance regions 72 are arranged at the same position on the front surface and the back surface, the wall surface of the hole becomes vertical to the surface, and if they are arranged so as to be displaced, the wall surface becomes oblique. [Embodiment 4] FIG. 4 shows an example of a case where the surface of non-porous Si is made to have a high resistance, and the exposed low resistance part is made porous from the back surface.

As shown in FIG. 4A, non-porous Si8
The surface of No. 1 is partially made high in resistance to form a high resistance region 82. At least one low resistance region is exposed on each side. The high resistance region 82 is formed by a non-deposition method such as ion implantation or impurity diffusion.

Next, the exposed low resistance portion and the back surface are made porous (FIG. 4B).

After that, only one of the above four kinds of etching solutions is used to selectively remove the porous Si region 83 by wet chemical etching.

FIG. 4C shows a completed diagram of this embodiment. As described above, the holes can be partially penetrated from the front surface to the back surface of the non-porous Si at one or more locations.

[0088]

Embodiments of the present invention will be described in detail below with reference to the drawings. Example 1 A high resistance epitaxial Si layer is formed on both surfaces of a 200 μm thick low resistance single crystal Si substrate by MBE (Molecular Beam Epitaxy).
It was formed to a thickness of 0.5 μm by the axy method. The growth conditions are
It is as follows.

Temperature: 700 ° C. Pressure: 1 × 10 ⁻⁹ Torr Growth rate: 0.1 nm / sec After that, a resist is patterned on the epitaxial Si layer by a lithography technique to form an epitaxial Si layer.
RIE (Reactive Ion Etching: React) is performed until the low resistance single crystal Si substrate is exposed in the region where the layer is exposed.
It was etched by the iv lon Etching method. At this time, at least one exposed low resistance region was present on each surface. Further, the exposed low resistance region was arranged at the same position on the front and back surfaces in the plane. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1:
1: 1 time: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The maskless portion from the front surface to the back surface was made porous.
This substrate was buffered with hydrofluoric acid (4.5% HF + 36% N
H ₄ F + H ₂ O) and stirred. After 258 minutes, only the porous Si was selectively removed, and a single-crystal Si substrate partially having at least one hole penetrating to the back surface was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are
It was determined only by the mask pattern, and its size was limited only to the size of the substrate used.

A high resistance epitaxial Si film was used for the mask of this example, but similar results were obtained with other materials such as a coating layer, a deposited film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization. (Embodiment 2) High resistance epitaxial Si layers are formed on both surfaces of a 200 μm thick low resistance single crystal Si substrate under reduced pressure CVD (Chemical Vapor Deposition: Chemical Vapor Depo).
The film thickness was 0.5 μm. The growth conditions are as follows.

Source gas: SiH ₄ Carrier gas: H ₂ Temperature: 850 ° C. Pressure: 1 × 10 ⁻² Torr Growth rate: 3.3 nm / sec After that, a resist is patterned on the epitaxial Si layer by a lithography technique to form an epitaxial Si layer.
RIE (Reactive Ion Etching: React) is performed until the low resistance single crystal Si substrate is exposed in the region where the layer is exposed.
It was etched by the iv lon Etching method. At this time, at least one exposed low resistance region was present on each surface. Further, the exposed low resistance region was arranged at the same position on the front and back surfaces in the plane. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The portion without a mask from the front surface to the back surface was made porous.
This substrate was buffered with hydrofluoric acid (4.5% HF + 36% N
(H ₄ F + H ₂ O) and alcohol (10: 1) were infiltrated. After 275 minutes, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained.
The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the mask pattern, and the size is limited only to the size of the substrate used.

Although the high resistance epitaxial Si film was used for the mask of this example, similar results were obtained with other materials, such as a coating layer deposition film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization. (Embodiment 3) A high resistance epitaxial Si layer is formed on both surfaces of a low resistance single crystal Si substrate having a thickness of 200 μm by LPE (Liquid Phase Epitaxy).
It was formed to 3 μm by the y) method. The growth conditions are as follows.

Solvent: Sn Growth temperature: 900 ° C. Growth atmosphere: H ₂ Growth time: 30 min After that, a resist is patterned on the epitaxial Si layer by a lithography technique to form epitaxial Si.
RIE (Reactive Ion Etching: React) is performed until the low resistance single crystal Si substrate is exposed in the region where the layer is exposed.
It was etched by the iv lon Etching method. At this time, at least one exposed low resistance region was present on each surface. Further, the exposed low resistance region was arranged at the same position on the front and back surfaces in the plane. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The portion without a mask from the front surface to the back surface was made porous.
This substrate was buffered with hydrofluoric acid (4.5% HF + 36% N
The mixture was infiltrated with a mixed solution of H ₄ F + H ₂ O) and 30% hydrogen peroxide solution (1: 5), and stirred. After 191 minutes, only porous Si was selectively removed, and holes penetrating to the back surface were
Single crystal Si partially formed in at least one place
A substrate was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the mask pattern, and the size is limited only to the size of the substrate used.

A high resistance epitaxial Si film was used for the mask of this example, but similar results were obtained with other materials such as a coating layer, a deposited film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization. Example 4 A high resistance epitaxial Si layer having a thickness of 0.5 μm was formed on both surfaces of a low resistance single crystal Si substrate having a thickness of 200 μm by a bias sputtering method. The growth conditions are as follows.

RF frequency: 100 MHz High frequency power: 600 W Ar gas pressure: 8 × 10 ⁻³ Torr DC bias: −200 V Substrate DC bias: +5 V Temperature: 300 ° C. Growth time: 60 min After that, resist was formed on the epitaxial Si layer by a lithography technique. Patterned to form epitaxial Si
RIE (Reactive Ion Etching: React) is performed until the low resistance single crystal Si substrate is exposed in the region where the layer is exposed.
It was etched by the iv lon Etching method. At this time, at least one exposed low resistance region was present on each surface. Further, the exposed low resistance region was arranged at the same position on the front and back surfaces in the plane. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The portion without a mask from the front surface to the back surface was made porous.
This substrate was buffered with hydrofluoric acid (4.5% HF + 36% N
H ₄ F + H ₂ O), alcohol and 30% hydrogen peroxide solution (10: 6: 50) were infiltrated. After 205 minutes, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the mask pattern, and the size is limited only to the size of the substrate used.

A high resistance epitaxial Si film was used for the mask of this example, but similar results were obtained with other materials such as a coating layer, a deposited film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization. Example 5 Apiezon wax was partially coated on both surfaces of a 200 μm thick low resistance single crystal Si substrate. At this time, at least one exposed low resistance region was present on each surface. Further, the exposed low resistance region was arranged at the same position on the front and back surfaces in the plane. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1:
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The portion without a mask from the front surface to the back surface was made porous.
This substrate was buffered with hydrofluoric acid (4.5% HF + 36% N
H ₄ F + H ₂ O), alcohol and 30% hydrogen peroxide solution (10: 6: 50) were infiltrated. After 205 minutes, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the mask pattern, and the size is limited only to the size of the substrate used.

Although the mask of this example uses apiazone wax, similar results were obtained with other materials such as a coating layer, a deposited film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization. (Embodiment 6) 1 μm polyimide was applied as a mask on both surfaces of a 200 μm thick low resistance single crystal Si substrate to form a mask. At this time, there was at least one exposed Si region on each surface. Also, exposed Si
The regions were arranged offset on the front and back surfaces. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) The portion without a mask from the front surface to the back surface was made porous.
After removing the polyimide of the mask, the substrate was soaked in a mixed solution of buffered hydrofluoric acid (4.5% HF + 36% NH ₄ F + H ₂ O), alcohol and 30% hydrogen peroxide solution (10: 6: 50). did. After 205 minutes, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. The wall surface of this hole was inclined with respect to the surface by the amount of deviation of the opening of the mask. Here, the shape and size of the opening of the hole are determined only by the mask pattern, and the size is limited only to the size of the substrate used.

Polyimide was used for the mask of this example, but similar results were obtained with other materials such as a coating layer, a deposited film or an epitaxial film having high resistance and high hydrofluoric acid resistance.
At this time, the mask may be peeled off after the anodization. (Embodiment 7) A high resistance epitaxial Si layer is provided on one surface of a 200 μm thick low resistance single crystal Si substrate by MBE (Molecular Beam Epitaxy).
It was formed to a thickness of 0.5 μm by the xy) method. The growth conditions are as follows.

Temperature: 700 ° C. Pressure: 1 × 10 ⁻⁹ Torr Growth rate: 0.1 nm / sec After that, a resist is patterned on the epitaxial Si layer by a lithography technique to form an epitaxial Si layer.
RIE (Reactive Ion Etching: React) is performed until the low resistance single crystal Si substrate is exposed in the region where the layer is exposed.
It was etched by the iv lon Etching method. At this time, at least one exposed low resistance region was present on each surface. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) Porous was made from the front surface to the back surface through a portion without a mask. This substrate was buffered with hydrofluoric acid (4.5% HF + 3
6% NH ₄ F + H ₂ O), alcohol and 30% hydrogen peroxide solution (10: 6: 50) were infiltrated. 205
After a minute, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. Here, the shape and size of the opening of the hole are determined only by the mask pattern,
The size was limited only to the size of the substrate used.

A high resistance epitaxial Si film was used for the mask of this example, but similar results were obtained with other materials, such as a coating layer, a deposited film or an epitaxial film having high resistance and strong hydrofluoric acid resistance. At this time, the mask may be peeled off after the anodization.

Although the selective etching solution of this example was a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide, the same results were obtained with the other three kinds of etching solutions described in the example of the embodiment. Was given. (Embodiment 8) 200 μm thick P-type low resistance (1 × 10 ¹⁹ c
m ^-3 ) A high resistance region was formed on both surfaces of the single crystal Si substrate by masking with a resist and ion-implanting the opening, followed by heat treatment. The implantation and heat treatment conditions were as follows.

Ion species: P ⁺ energy: 120 keV Implantation amount: 2 × 10 ¹⁴ cm ^-2 Heat treatment: 900 ° C., 30 min At this time, at least one low resistance region not ion-implanted exists on each surface. It was Further, the low resistance region was arranged in the same position on the front and back surfaces. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Porous Si thickness: 200 (μm) Porosity: 56 (%) From the front surface to the back surface, the portion not ion-implanted was made porous. This substrate is buffered with hydrofluoric acid (4.5% HF
+ 36% NH ₄ F + H ₂ O) and stirred. Two
After 58 minutes, only the porous Si was selectively removed, and a single-crystal Si substrate partially having at least one hole penetrating to the back surface was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region in this example, similar results were obtained by the diffusion method. (Example 9) 200 μm thick P-type low resistance (2 × 10 ¹⁷ c
m ^-3 ) A high resistance region was formed on both surfaces of the single crystal Si substrate by masking with a resist and ion-implanting the opening, followed by heat treatment. The implantation and heat treatment conditions were as follows.

Ion species: H ⁺ energy: 100 keV Implantation amount: 2 × 10 ¹⁵ cm ⁻² Heat treatment: 500 ° C., 30 min At this time, at least one low resistance region not ion-implanted exists on each surface. It was Further, the low resistance region was arranged in the same position on the front and back surfaces. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Porous Si thickness: 200 (μm) Porosity: 56 (%) From the front surface to the back surface, the portion not ion-implanted was made porous. This substrate is buffered with hydrofluoric acid (4.5% HF
+ 36% NH ₄ F + H ₂ O) and alcohol (10:
It was infiltrated in the mixed solution with 1). After 275 minutes, the porous S
Only i was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. The wall of this hole was perpendicular to the surface.
Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region in this example, similar results were obtained by the diffusion method. (Example 10) 200 μm thick N-type low resistance (1 × 10 ¹⁹
cm ⁻³ ) A single-crystal Si substrate was masked with a resist on both sides thereof, and its opening was ion-implanted, followed by heat treatment to form a high resistance region. The implantation and heat treatment conditions were as follows.

Ion species: B ⁺ energy: 150 keV Implantation amount: 4 × 10 ¹⁴ cm ^-2 Heat treatment: 900 ° C., 30 min At this time, at least one low resistance region not ion-implanted exists on each surface. It was Further, the low resistance region was arranged in the same position on the front and back surfaces. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Porous Si thickness: 200 (μm) Porosity: 56 (%) From the front surface to the back surface, the portion not ion-implanted was made porous. This substrate is buffered with hydrofluoric acid (4.5% HF
The mixture was infiltrated with a mixed solution of + 36% NH ₄ F + H ₂ O) and 30% hydrogen peroxide solution (1: 5) and stirred. After 191 minutes, only the porous Si was selectively removed, and a single crystal Si substrate partially formed with at least one hole penetrating to the back surface was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region in this example, similar results were obtained by the diffusion method. (Example 11) 200 μm thick P-type low resistance (1 × 10 ¹⁹
cm ⁻³ ) A single-crystal Si substrate was masked with a resist on both sides thereof, and its opening was ion-implanted, followed by heat treatment to form a high resistance region. The implantation and heat treatment conditions were as follows.

Ion species: P ⁺ energy: 120 keV Implantation amount: 2 × 10 ¹⁴ cm ^-2 Heat treatment: 900 ° C., 30 min At this time, at least one low resistance region not ion-implanted exists on each surface. It was Further, the low resistance region was arranged in the same position on the front and back surfaces. This formed a mask for leaving the non-porous Si region in the subsequent anodization.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Porous Si thickness: 200 (μm) Porosity: 56 (%) From the front surface to the back surface, the portion not ion-implanted was made porous. This substrate is buffered with hydrofluoric acid (4.5% HF
+ 36% NH ₄ F + H ₂ O), alcohol and 30% aqueous hydrogen peroxide (10: 6: 50). Two
After 05 minutes, only the porous Si was selectively removed, and a single-crystal Si substrate partially formed with at least one hole penetrating to the back surface was obtained. The wall of this hole was perpendicular to the surface. Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region of this example, similar results were obtained by the diffusion method. (Example 12) 200 μm thick P-type low resistance (1 × 10 ¹⁹
cm ⁻³ ) A single-crystal Si substrate was masked with a resist on both sides thereof, and its opening was ion-implanted, followed by heat treatment to form a high resistance region. The implantation and heat treatment conditions were as follows.

Ion species: P ⁺ energy: 120 keV Implantation amount: 2 × 10 ¹⁴ cm ⁻² Heat treatment: 900 ° C., 30 min At this time, at least one or more low-resistance regions not ion-implanted exist on each surface. It was Further, the low resistance regions are arranged so as to be offset on the front surface and the back surface. This formed a mask for leaving the non-porous Si region in the subsequent anodization. Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 30 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 1.6 (hours) Porous Si thickness: 200 (μm) Porosity: 56 (%) From the front surface to the back surface, the portion not ion-implanted was made porous. This substrate is buffered with hydrofluoric acid (4.5% HF
+ 36% NH ₄ F + H ₂ O), alcohol and 30% aqueous hydrogen peroxide (10: 6: 50). Two
After 05 minutes, only the porous Si was selectively removed, and a single-crystal Si substrate partially formed with at least one hole penetrating to the back surface was obtained. The wall surface of this hole was inclined with respect to the surface by the amount of deviation of the opening of the mask. Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region in this example, similar results were obtained by the diffusion method. (Example 13) 200 μm thick P-type low resistance (1 × 10 ¹⁹
A mask was formed on one surface of the cm ⁻³ ) single crystal Si substrate with a resist, the opening was ion-implanted, and the heat treatment was performed thereafter to form a high resistance region. The implantation and heat treatment conditions were as follows.

Ion species: P ⁺ energy: 120 keV Implantation amount: 2 × 10 ¹⁴ cm ^-2 Heat treatment: 900 ° C., 30 min At this time, at least one or more low-resistance regions not ion-implanted exist on each surface. It was by this,
The next anodization formed a mask to leave the non-porous Si regions.

Anodization was performed in the HF solution.

The anodization conditions were as follows.

Current density: 15 (mA · cm ⁻² ) Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1
1 hour: 2.6 (hours) Thickness of porous Si: 200 (μm) Porosity: 56 (%) Porous was conducted from the front surface to the back surface through a portion not ion-implanted. This substrate was buffered with hydrofluoric acid (4.5
% HF + 36% NH ₄ F + H ₂ O) and alcohol and 30
% Hydrogen peroxide solution (10: 6: 50). After 205 minutes, only the porous Si was selectively removed, and a single crystal Si substrate in which at least one hole penetrating to the back surface was partially formed was obtained. Here, the shape and size of the opening of the hole are determined only by the pattern at the time of ion implantation, and the size is limited only to the size of the substrate used.

Although the ion implantation method was used for forming the high resistance region in this example, similar results were obtained by the diffusion method.

As the selective etching solution of this example, a mixed solution of buffered hydrofluoric acid, alcohol and hydrogen peroxide was used, but the same results can be obtained with the other three kinds of etching solutions listed in the example of the embodiment. Was obtained.

[0153]

As described in detail above, according to the present invention,
Applicable to normal semiconductor process and non-porous Si
Is a buffered hydrofluoric acid that does not etch, or a solution obtained by mixing buffered hydrofluoric acid with at least one of alcohol and hydrogen peroxide water as a wet chemical etching liquid.
The non-porous Si substrate is processed by selectively and chemically etching the porous Si region, which is partially provided in one or more places in the non-porous Si substrate, with high accuracy and in an arbitrary shape. With the size of, it becomes possible to make a hole penetrating from the front surface to the back surface.

Particularly, by adding alcohol, the bubbles of the reaction product gas due to etching can be instantly removed from the etching surface without stirring, and the porous Si can be uniformly and efficiently etched extremely flatly. can do.

By adding hydrogen peroxide solution, the oxidation of silicon can be accelerated and the reaction rate can be increased as compared with the case of no addition, and by changing the ratio of hydrogen peroxide solution. , Its reaction rate can be controlled.

Since the porous Si used in the present invention is formed along the current flow at the time of anodization, the current flow can be controlled by providing a mask or an impurity distribution, and it is almost arbitrary. It is possible to process the non-porous Si into the shape of.

Further, according to the present invention, the non-porous Si substrate is partially transformed into porous Si at one or more places, and the etching solution is used very efficiently and highly accurately without using an etching preventive film. It becomes possible to remove the porous Si region and form a region partially penetrating to the back surface at one or more places in the non-porous Si substrate.

Furthermore, according to the present invention, a light transmissive substrate,
Also, it becomes possible to produce an article applicable to micromachining and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a basic process of a first embodiment example of the present invention.

FIG. 2 is a sectional view showing a basic step of a second embodiment of the present invention.

FIG. 3 is a sectional view showing a basic step of the third embodiment of the present invention.

FIG. 4 is a sectional view showing a basic step in a fourth embodiment of the present invention.

FIG. 5 shows etching characteristics of porous and non-porous Si with buffered hydrofluoric acid.

FIG. 6 shows etching characteristics of porous and non-porous Si with a mixed solution of buffered hydrofluoric acid and alcohol.

FIG. 7 shows etching characteristics of porous and non-porous Si with a mixed solution of buffered hydrofluoric acid and hydrogen peroxide solution.

FIG. 8 shows etching characteristics of porous and non-porous Si with a mixed solution of buffered hydrofluoric acid, alcohol, and hydrogen peroxide solution.

[Explanation of symbols]

 51 non-porous Si substrate 52 mask 53 porous Si region 61 non-porous Si substrate 62 mask 63 porous Si region 71 low resistance non-porous Si substrate 72 high resistance Si region 73 porous Si region 81 low resistance non-porous Si substrate 82 High resistance Si region 83 Porous Si region

Claims (3)

[Claims] 1. A step of partially porosifying a non-porous Si substrate from one surface to a back surface, and a non-porous S.
By infiltrating a substrate in which the i region and the porous Si region coexist with buffered hydrofluoric acid or a mixed liquid of buffered hydrofluoric acid with at least one selected from alcohol and hydrogen peroxide water, And a step of selectively etching and removing only the Si region, the method for processing a Si substrate. 2. The method for processing a Si substrate according to claim 1, wherein the step of making porous is anodization. 3. The method for processing a Si substrate according to claim 2, wherein the anodization is performed in an HF solution.